Reproduced below is the text from the catalogue for the section "Collecting Copyright Stamps"
Copyright stamps represent an exciting new branch of Revenue philately. I use the word "exciting" because of the large range of issuers from all parts of the world, the certainty of making new finds, the wide variety of interesting designs and the scope for philatelic specialisation in printings, papers, perforations and varieties, especially in some of the major issuers.
I have also used the term Revenue rather than Cinderella as these items were clearly issued "under the origination authority of a state ... authority" per the F.I.P. Special Regulations for the Evaluation of Revenue Exhibits.
The stamps are still readily available on their original source, be that 78rpm records, piano rolls, and the sleeves and labels of early LP and 45rpm records. Other sources with less frequent chance of 'finds' include sheet music, cylinder boxes and the books of R.L. Stevenson.
As this is a new branch of Revenue collecting, there is still much that is unknown or uncertain, particularly as pertaining to the date of use of many items. Until printing and usage records are uncovered from the many issuers and their printers, the only means to determine this remains the dating of the item on which the stamp was affixed. While impractical to retain a complete collection 'on piece', once the stamp is removed the critical link is gone.
I recommend using a notebook to record, by number, key details of the item on which the stamp appears and writing the corresponding entry number lightly in pencil on the back of the stamp. Key items would be record issuer, serial number and matrix, e.g. HMV B2340 OE013246. The artist, track and composer are also useful, particularly where there is an overprint. Taking a digital photo or scan of each item prior to removal would be ideal, but it is not always practical.
Ideally, the stamp should be retained on the item to which it belongs. As the stamps are not tied, subsequently proving this juxtaposition is near impossible.
In general though, the stamps will be soaked from the 78s or rolls on which they reside. This certainly makes sense for 78s, which are bulky and hard to display in any volume (although the occasional item in an exhibit will be attractive). Piano rolls cannot be displayed in a normal philatelic exhibition frame, yet frequently they have attractive multiples or mixed frankings - medleys were much commoner on rolls than on early records.
Cutting off the last 8" or so of the tongue is a happy compromise, and a new paper tongue can be applied to the 'vandalised' roll if it is worth retaining for its musical value. 12" LP sleeves are problematic, but 10" and 45rpm sleeves will fit in an exhibition frame.
There is little to be gained by retaining common stamps on entire or piece. However, very rare or unique items should be if at all possible, until catalogued at least. All items suspected of being a new find, or a good example of a rare item should be Xeroxed or scanned or photographed for posterity and to assist future researchers. A rare stamp on its visibly correct item, especially if exhibitable, will obviously attract a premium.
Removal of the stamps can be done by cutting small square of blotting paper, soaking in a bowl of luke-warm water with 1-2 drops of detergent mixed in, and placing over the stamp. After 5-10 minutes most stamps will slide off. Some record labels do not have water-fast inks and this will cause a stain of varying degrees to the back, and sometimes edges of the stamp. This can be minimised by the alternative method of soaking the complete record in a bath of very lukewarm water. Some other records should never be immersed in water, if the record is to be preserved, especially Edison Diamond Discs (the 1/4" thick ones), acetates (often with an aluminium core) and any that appear to be made of laminated card, such as Durium and some Duophones.
Some record labels use a gold ink that appears to bond very tightly with the glue used on most stamps, making it nearly impossible to remove without either thinning the stamp, or damaging the record label itself. ACO records are particularly bad in this regard.
Finally, the striking early issues of the SociÃ©tÃ© GÃ©nÃ©rale, especially when applied to PathÃ© records circa 1910-18, utilised a glue that defies attempts to soften it. The record label will either need to be sacrificed, and will always leave an unsightly adherence to the back of the stamp, or the stamp will start to disintegrate before it lifts. As these early PathÃ© records are often quite expensive and desirable in their own right, I tend to leave them as found.
There is always the possibility that collecting the stamps will also lead on to collecting the old records. As with stamp collecting, many organisations exist to assist those afflicted, so don't let this possibility deter you!